1. Field of the Invention
The present invention relates to a method for testing the fuel quantity balance in a common rail system, a corresponding engine control system, and a corresponding diagnostic device, e.g., for motor vehicles, having two electrically controlled actuating elements, namely a metering unit at the input side of a high-pressure pump and a pressure regulating valve on the common rail.
2. Description of the Related Art
Defects in the low-pressure circuit, pump defects, or defects in other components of the high-pressure circuit of a common rail fuel supply system can cause a reduced fuel delivery rate. Such defects often first appear when delivery rates are present that are greater than the idling delivery rate. Causes of low delivery rate can include, among others, a clogged fuel filter, internal or external high-pressure leaks, piston wear (blow-by), or a defective, uptight intake or high-pressure valve of the high-pressure injection pump. Currently, for workshop diagnosis of the fuel supply system, there are available on the one hand invasive component-specific diagnostic tests that permit conclusions to be drawn, e.g. concerning the pump delivery rate, at specific test points on an external workshop test device, or that permit invasive non-component-specific tests of the low-pressure circuit (e.g. low-pressure measurement).
On the other hand, non-invasive diagnostic tests are used, for example a tightness test for the common rail system as proposed in published European patent application document EP 1 186 775 A2, or a test for uneven delivery as disclosed in published German patent application document DE 10 2008 001 182 A1.
In general, the diagnostic methods currently used in the workshop do not permit diagnostic conclusions to be reached without invasive intervention in the vehicle, in particular in the case of target delivery rates that are greater than the delivery rate of the pump during idling operation of the vehicle.